The invention relates generally to the field of image sensing IC chip packages and methods of making same.
An image sensing integrated circuit chip 23, shown in FIG. 1, is at the center of all electronic, i.e. digital, cameras. Typically, IC chip package 23 is ceramic and has a glass window 25 covering an image sensitive integrated circuit die 29. As it is known in the art, image sensitive circuit die 29 may include an array of light sensitive charge coupled devices that produce an electronic image when exposed to light. Glass window 25 is part of a standard xe2x80x9ccoverxe2x80x9d or xe2x80x9clidxe2x80x9d for the IC chip 23 and has the sole function of providing a hermetic seal to protect circuit die 29 from the environment while permitting it to be exposed to light. Image sensing IC chip package 23, however, is only a small part of an electronic camera.
With reference to FIG. 2, the imaging module 9 of a typical electronic camera incorporates several components and sub-components. The components are assembled into a carrier package for the individual sub-components. FIG. 2 provides a cut-out view of a typical image module assembly, or carrier package, 9. As shown, carrier package 9 includes a lens assembly 11, a mounting plate 15 and a ceramic, IC chip package 19 housing a solid state image sensitive die 22. As explained above, ceramic chip 19 has a glass window 21 over the image sensitive die 22. The cavity 13 of lens assembly 11 typically includes such elements as an aperture, an optical lens, and an IR filter. A recessed barrel 11b of lens assembly 11 would be fitted into an opening in mounting plate 15, which in turn would have multiple reference locators 17 for mating with concentric mounting holes 24 in ceramic chip package 19. The assembly of carrier package 9 is further complicated by the requirement that the optical lens be kept at a critical xe2x80x9cfocal distancexe2x80x9d to the surface of the image sensitive die 22. A further discussion on some of the difficulties associated with construction of such imaging modules can be found in U.S. Pat. No. 5,998,878.
In addition to the complexity of imaging module 9, the image sensing IC chip package 19 can place additional obstacles to the construction of an electronic camera. As explained above, IC chip package 19 is typically ceramic, which makes it considerably more expensive than other IC chip packages. Attempts to reduce the cost of packaging an image sensitive die has lead to the use of plastic chip packages in electronic cameras.
FIG. 3 shows an example of a plastic chip package 31 for housing an image sensitive die 33 discussed in U.S. Pat. No. 5,534,745. Image sensitive die 33 is attached to a substrate paddle 35. As it would be understood in the art, the light sensitive charge coupled devices, CCD, would be arranged in an array pattern in the middle of the surface of die 33. For illustrative purposes, the side-view of the section of die 33 representing the CCD array is shown as a rectangular shape 39 along the top surface of die 33. In the present example, a film wall 41 of polyamide having adhesive on both its upper and lower sides is placed surrounding the image sensitive area 39 of die 33. A glass cover 43 is then attached onto the film wall 41 over the image sensitive area 39 of die 33. Wire leads 37 are then bonded to the bond pads on die 33. Finally, the entire assembly is encased in a molding step to form plastic package 31.
A second approach to produce a plastic chip package for an image sensitive die is discussed in U.S. Pat. No. 5,753,857. With reference to FIG. 4, an IC chip package 51 in accordance with the ""857 patent consists of two interlocking, plastic components; a support-base component 53 and a lid component 55. The image sensitive die 57 is attached to base component 53. The lid component 55 includes solder bumps 59 coupled to wire leads 61. As the lid component 55 is coupled to the support-base component 53, the solder bumps 59 line up with the bond pads on image sensitive die 57. The lid component 55 also has an opening on top exposing the CCD array 58 of die 57. Once the lid component 55 and support-base component 53 have been assembled, a glass top 63 is adhered to lid component 55.
None of the preceding examples, however, attempt to simplify the basic imaging module assembly 9 shown in FIG. 2. One approach toward simplifying a imaging module assembly is to incorporate one of the sub-components of the lens assembly into an IC chip package itself. U.S. Pat. No. 5,340,420 is an example of this approach.
With reference to FIG. 5, the approach described in the ""420 patent is to incorporate a color separation filter 65 into an image sensitive, IC chip package 67. Image sensitive die 69 is placed within chip package 67 and wire bonds 71 couple bond pads on die 69 to wire leads within chip package 67. Following this, an optical coupling composition 73 is uniformly coated on top of image sensitive die 69. A color separation filter 65 is then placed on composition 73. Filter 65 is pressed down to form uniform spreading of composition 73, and is then aligned using alignment targets, as is known in the art. Once the die 69 and filter 65 assembly has been checked for debris and bubble entrapment, very small amounts of ultraviolet curable adhesive is placed at each end of filter 65 to set it in place. A black epoxy is then dispensed along the periphery of filter 65 to encapsulate the separation interface between filter 65 and die 69. Lastly, a glass cover 75 is placed on IC chip package 67.
In spite of the incorporation of the filter into the IC package, as shown in FIG. 5, one is still required to construct a larger imaging module assembly 9, as shown in FIG. 2, to house all the other necessary sub-components of the lens module 11 and to attach the lens module to the chip package. What is needed is an IC chip package that minimizes the need for construction of a modular imaging assembly.
It is an object of the present invention to provide an imaging module assembly of reduced complexity.
It is a second object of the present invention to reduce the cost associated with the construction of an imaging module assembly.
It is still a third object of the present invention to provide a method of miniaturizing the imaging assembly of an electronic camera.
The above objects have been met in a one-piece, chip module cover design that integrates all the critical functional elements of the imaging module of an electronic camera. The electronic camera module of the present invention provides reduced piece parts and assembly costs by integration of all the individual sub-components of an imaging module and their respective mounting features into a single cover design for an IC chip package. As a result, the present invention also provides a higher reliability for the overall imaging module assembly of the camera.
The IC chip package of the present invention constitutes a complete imaging module for an electronic camera, and is preferably constructed from injection molded plastic to further reduce cost. A molded plastic cover is first constructed. The molded plastic cover holds an IR filter, holds an optical lens within proper focal distance, provides an aperture function for the optical lens, and provides protection for an image sensitive die, which it covers. Preferably the cover also has a metal coat, such as electroless nickel plating, to provide EMI shielding. The process begins by attaching the image sensitive die, or image sensor die, to a substrate carrier using a die attach epoxy. A wire bond operation is then executed to connect I/O bond pads on the die to substrate carrier bond fingers. A partially assembled, one piece molded chip cover is then attached to the substrate carrier using epoxy. UV cure adhesive is applied to a lens shelf constructed within the molded chip cover. An optical lens is then placed on the lens shelf of the molded chip cover. The focal distance of the lens to the image sensor die is aligned by activating the die and comparing the focus xe2x80x9csharpnessxe2x80x9d. Once the proper focal point is obtained, a UV light source is activated to xe2x80x9ccurexe2x80x9d the adhesive and hold the lens in focus. A filter glass is then placed on top of the cover. Finally, an epoxy seal process is used to seal the filter glass to the top of the molded cover. This assembly consists of two epoxy joints which has proven to form reliable seals.
Thus, the invention allows fabrication of a miniature camera module for portable electronics like cellular phone, pagers PC cameras etc.